After running your mower for awhile then shut it off it will not start?

sounds like the motor is over heating, check OIL, Level, run a thicker oil in summer, use standard 30 wt, oil

not a combination oil, like 10w-30 check air passages, screen on flywheel, , has it always done this? did it just start ? was it hot out side,?

had it rained lately ? did you hit something with the blade ? lot of factors can cause this,